Conventionally, perfusion images are generated by an X-ray Computed Tomography (CT) apparatus or a Magnetic Resonance Imaging (MRI) apparatus, so as to analyze, for example, dynamics of bloodstream in a brain tissue, a liver tissue, or a pancreas tissue. For example, the X-ray CT apparatus calculates chronological changes in CT values from X-ray CT images that are taken in time series and are of the head or the abdomen of an examined subject (hereinafter, “patient”) to whom a nonionic iodine contrast agent has been injected. Further, the X-ray CT apparatus generates a perfusion image in which an index indicating the dynamics of the bloodstream passing through the tissue is mapped on the tissue, on the basis of the calculated chronological changes in the CT values. According to the conventional technique described above, however, it is difficult to check the reliability of analysis results of the perfusion images.